Known X-ray CT scanners typically include an X-ray generator and an X-ray detector arranged opposite each other across a subject, and CT imaging is performed through irradiation and detection of X-rays while the X-ray generator and the X-ray detector are rotated relative to the subject. In the process of CT imaging, projection data indicating the degree of X-ray attenuation (degree of X-ray absorption by the subject) is collected at each rotational angle, and a tomographic image (CT image) of the subject is generated based on the obtained projection data.
During the process of CT imaging, if an imaging target site such as an organ moves due to body motion of the subject including respiratory motion, artifacts are generated in the final CT image. As such, respiratory synchronized scanning, in which respiratory motion of a subject is detected and CT imaging (scanning) is performed in synchronization with a phase where motion of the organ due to respiration is determined to be least likely, has been proposed in, for example, Japanese patent publications JP 2000-139892 A and JP 2006-311941 A (Patent Documents 1 and 2 listed below). By employing such an art, generation of artifacts due to body motion can be reduced, thereby enabling capturing of higher quality CT images.